1. Field of the Invention
This invention relates to a screening method and apparatus. This invention particularly relates to a screening method and apparatus for performing a screening operation in accordance with binding quantity data, each of which represents a quantity of binding of a ligand and an analyte with each other and each of which has been obtained with measurement utilizing a refractive index alteration occurring at an interface on a base body block.
2. Description of the Related Art
Ordinarily, the majority of compounds constituting pharmaceutical preparations fulfill their functions by undergoing chemical binding with proteins in living bodies. Therefore, for development of a pharmaceutical preparation, it is important to investigate whether a compound acting as a candidate for the pharmaceutical preparation is or is not capable of undergoing chemical binding with a protein. In particular, it is ideal that a compound constituting a pharmaceutical preparation has the binding ability with respect to only a protein of interest and does not have the binding ability with respect to the other proteins. Specifically, if the compound constituting the pharmaceutical preparation has the binding ability with respect to the proteins other than the protein of interest, the compound will have adverse side effects. In view of the above circumstances, in the field of the development of pharmaceutical preparations, screening operations have heretofore been performed for extracting a compound, which has the binding ability with respect to only a protein of interest, from compounds acting as the candidates for the pharmaceutical preparations.
Various types of apparatuses have heretofore been proposed for the screening operations performed on the compounds acting as the candidates for the pharmaceutical preparations. For example, there has been known an analysis apparatus for causing a surface plasmon to occur through total reflection of a light beam from a metal surface, and for making an analysis by the utilization of an alteration of a specific reflection angle, i.e. an attenuated total reflection angle (an ATR angle), which is associated with the occurrence of marked attenuation of an optical intensity (i.e., attenuated total reflection) in the light beam having been totally reflected from the metal surface, and which alters in accordance with a dielectric constant (or a refractive index) in the vicinity of the metal surface. (The aforesaid analysis apparatus is described in, for example, “Surface Refracto-sensor using Evanescent Waves: Principles and Instrumentations” by T. Okamoto, Spectrum Research, Vol. 47, No. 1, pp. 19-28, 1997.) Also, as an apparatus utilizing the principle of the surface plasmon described above, there has heretofore been known, for example, BIACORE 3000 supplied by Biacore K.K. (The apparatus utilizing the principle of the surface plasmon is described in, for example, “Methods of Experiments and Real-Time Analysis of Interaction with Biological Materials” by Kazuhiro Nagata & Hiroshi Handa, Published by Springer Verlag Tokyo K.K., pp. 27-34, 1998)
By use of the apparatuses of the types described above, studies have heretofore been made on techniques for obtaining measurement data, which represent binding quantities between a single kind of a protein and multiple kinds, e.g., 10,000 kinds, of compounds, and for extracting hit compounds, which are the compounds capable of undergoing the binding with the single kind of the protein, from the multiple kinds of the compounds and in accordance with the measurement data.
Ordinarily, the hit compounds, which are extracted with the compound screening operation as described above, are approximately 1% of the multiple kinds of the compounds subjected to the screening operation. Specifically, ordinarily, approximately 100 kinds of compounds are extracted as the hit compounds from 10,000 kinds of compounds subjected to the screening operation. Also, two to three days or more days are often required for the screening operation performed on the multiple kinds of the compounds.
As for the aforesaid analysis utilizing the attenuated total reflection, there has heretofore been known a technique, wherein an identical compound solution is retained on an actual measurement region, in which a protein has been fixed on a gold film having been formed on a surface of a transparent dielectric material block, and on a reference measurement region, in which the protein has not been fixed on the gold film, and wherein the quantity of binding of the compound, which is contained in the compound solution, and the protein with each other is measured. The quantity of the binding of the compound, which is contained in the compound solution, and the protein with each other is capable of being calculated from the difference between the ATR angle, which is measured when the compound solution is retained in the actual measurement region, and the ATR angle, which is measured when the compound solution is retained in the reference measurement region.
In cases where the protein and the compound are not capable of undergoing the binding with each other, the value of the measurement data representing the ATR angle, which is measured when the compound solution is retained in the actual measurement region, and the value of the reference measurement data representing the ATR angle, which is measured when the compound solution is retained in the reference measurement region, will coincide with each other, and the difference between the value of the measurement data and the value of the reference measurement data will be equal to 0. However, for reasons of the measuring system, or the like, it may often occur that the difference between the value of the measurement data and the value of the reference measurement data does not become equal to 0. For example, at the time of the measurement made in cases where the protein and the compound are not capable of undergoing the binding with each other, it may often occur that the difference between the ATR angle, which is measured when the compound solution is retained in the actual measurement region, and the ATR angle, which is measured when the compound solution is retained in the reference measurement region, alters in accordance with the magnitude of the refractive index of the compound solution to be analyzed.
Also, there has heretofore been studied a technique for correcting the difference between the ATR angle, which is measured when the compound solution is retained in the actual measurement region, and the ATR angle, which is measured when the compound solution is retained in the reference measurement region and which should fundamentally coincide with the aforesaid ATR angle measured in the actual measurement region. By way of example, the correction technique described below has heretofore been studied. Specifically, with the studied correction technique, multiple kinds of reference liquids having different refractive indexes are prepared. Also, with respect to each of the reference liquids, the difference between the ATR angle measured in the actual measurement region and the ATR angle measured in the reference measurement region is calculated. In this manner, the relationship between the refractive indexes of the reference liquids and the ATR angle differences having been found from the measurements is acquired. Further, the difference between the ATR angle measured in the actual measurement region and the ATR angle measured in the reference measurement region, which difference has been found from the measurements using the compound solution to be analyzed, is corrected in accordance with the relationship between the refractive indexes and the ATR angle differences, which relationship has been acquired by use of the reference liquids.
With the correction technique described above, reference is made to the relationship between the refractive indexes and the ATR angle differences, which relationship has been acquired by use of the reference liquids, and a variation of the difference between the ATR angle measured in the actual measurement region and the ATR angle measured in the reference measurement region, which difference arises in the measurements using the compound solution to be analyzed, is thereby presumed. In accordance with the presumed variation of the difference between the ATR angles, the variation of the difference between the ATR angle measured in the actual measurement region and the ATR angle measured in the reference measurement region is capable of being corrected.
However, the problems described below are encountered with the correction technique described above. Specifically, at the time at which the relationship between the refractive indexes and the ATR angle differences is acquired by use of the reference liquids, a variation of the environmental temperature, a variation of the concentrations (a variation of the refractive indexes) of the reference liquids due to evaporation, and the like, occur. Therefore, it is not always possible to acquire the accurate relationship between the refractive indexes and the ATR angle differences. Also, in cases where it is intended to obtain a large quantity of measurement data such that the relationship between the refractive indexes and the ATR angle differences may be acquired accurately, the measurements for the compound solutions to be subjected to the screening operation are not capable of being performed promptly, and the operation efficiency of the screening apparatus is not capable of being kept high. Therefore, there is a strong demand for a technique, with which the variation of the difference between the ATR angle measured in the actual measurement region and the ATR angle measured in the reference measurement region is capable of being corrected more accurately, and with which the reliability of the screening operation is capable of being enhanced, such that the efficiency of the screening operation may not become low.
The problems described above are encountered in cases where the screening operation is performed in accordance with the quantity of the binding of the ligand and the analyte with each other, which quantity of the binding has been obtained with measurements utilizing the ATR angle. The problems described above are also encountered in cases where the screening operation is performed in accordance with the quantity of the binding of the ligand and the analyte with each other, which quantity of the binding has been obtained with measurements utilizing the refractive index alteration occurring at the interface on the base body block.